1. The proximity switch is a position switch that can be operated in mechanical contact with a moving component. The proximity switch is a switch type sensor (ie, no contactless switch), which has the characteristics of a stroke switch and a micro switch. Simultaneous sensing performance and reliable operation
Stable performance, fast frequency response, long application life, strong anti-interference ability, and waterproof, shockproof and corrosion resistant. Products are inductive, capacitive, Hall, AC, DC.
The proximity switch, also known as the non-contact proximity switch, is an ideal electronic switching sensor.
2. The main function of the proximity switch
2.1 Inspection distance
Detecting the stop, start and pass position of the elevator and lifting equipment; detecting the position of the vehicle to prevent collision of two objects; detecting the set position of the working machine, moving the limit position of the machine or component; detecting the stop position of the rotary body, the valve Open or close position;
Detect the position of the piston in the cylinder or cylinder.
2.2 size control
The size control device for metal plate punching; automatically selects and identifies the length of the metal piece; detects the height of the pile during automatic loading and unloading; and detects the length, width, height and volume of the article.
2.3 Check the presence of objects Check whether there are product packaging boxes on the production packaging line; check for product parts.
2.4 speed and speed control
Control the speed of the conveyor; control the speed of the rotating machine; control the speed and number of revolutions with various pulse generators.
2.5 counting and control
Detect the number of products flowing through the production line; the number of revolutions of the rotating shaft or disk at high speed; the count of parts.
2.6 detection abnormality
Check the presence or absence of the bottle cap; judge the product's pass and fail; test the lack of metal products in the package; distinguish metal and non-metal parts; product with or without signage detection; crane danger zone alarm; safety escalator automatically start and stop.
2.7 Measurement Control
Automatic metering of products or parts; detecting the range of pointers of gauges and meters and controlling the number or flow; detecting buoys to control the height of the measuring surface, flow rate; detecting iron buoys in stainless steel barrels; controlling the upper or lower limit of meter range; flow control, horizontal control.
2.8 Identifying objects
Identify the right and wrong according to the code on the carrier.
2.9 Information transmission
The ASI (bus) connects the sensors at various locations on the device to and from the data line in the production line (50-100 meters).
3. Proximity switch classification and structure
The function of the proximity switch is to signal when an object approaches the proximity switch and reaches a certain distance. It does not require external force to apply and is a non-contact master electric appliance. Its use has far exceeded the travel control and limit protection of the travel switch.
Proximity switches can be used for high speed counting, detecting the presence of metal bodies, speed measurement, level control, detecting part sizes, and acting as contactless buttons. The currently widely used proximity switches can be classified into the following types according to the working principle:
High frequency oscillation type: used to detect various metal bodies
Capacitive type: used to detect various conductive or non-conductive liquids or solids
Photoelectric type: used to detect all opaque substances
Ultrasonic type: used to detect substances that do not transmit ultrasonic waves
Electromagnetic induction type: used to detect magnetic or non-magnetic metal
According to its shape, it can be divided into cylindrical type, square type, groove type, perforated (through) type and separated type. The cylindrical type is easy to install, but its detection characteristics are the same. The detection part of the groove type is inside the groove, which is used to detect the objects passing through the groove.
Less production, but Japan is more common, can be used for small parts such as screws or balls and buoys assembled into water level detection devices.
The proximity switch can be divided into two types according to the power supply mode: DC type and AC type. According to the output type, it can be divided into DC two-wire system, DC three-wire system, DC four-wire system, AC two-wire system and AC three-wire system.
3.1 two-wire proximity switch
The two-wire proximity switch is simple to install and convenient to wire; it is widely used, but has the disadvantage of large residual voltage and leakage current.
3.2 DC three-wire type
The output types of DC three-wire proximity switches are NPN and PNP. Most of the Japanese products in the 1970s were NPN outputs, and NPN and PNP are available in Western European countries. PNP output proximity switches are generally used in plc or computer as control commands.
The NPN output proximity switch is used to control more DC relays. In practical applications, the output form should be selected according to the characteristics of the control circuit.
4. Proximity switch selection and detection
4.1. Selection of proximity switches
For different material detectors and different detection distances, different types of proximity switches should be used to make them have high performance-price ratio in the system. For this reason, the following principles should be followed in the selection:
4.1.1. When the test object is a metal material, a high-frequency oscillation type proximity switch should be selected. This type of proximity switch is most sensitive to the detection of iron-nickel and A3 steel samples. For aluminum, brass and stainless steel samples, the detection sensitivity is low.
4.1.2. When the test object is a non-metallic material, such as wood, paper, plastic, glass and water, a capacitive proximity switch should be used.
4.1.3. For long-distance detection and control of metal and non-metal, photoelectric proximity switches or ultrasonic proximity switches should be used.
4.1.4. When the test object is metal, if the detection sensitivity is not high, a low-cost magnetic proximity switch or a Hall-type proximity switch may be used.
4.2. Proximity switch technical indicator detection
4.2.1. Determination of the action distance; when the action piece is close to the induction surface of the proximity switch, the distance of the proximity switch is close to the maximum action distance of the switch, and the measured data should be within the parameter range of the product.
4.2.2. Determination of the release distance; when the action piece leaves the sensing surface of the proximity switch from the front, and the switch is turned from the action to the release, the maximum distance of the action piece from the sensing surface is determined.
4.2.3. Determination of the hysteresis H; the absolute value of the difference between the maximum action distance and the release distance.
4.2.4. Determination of action frequency; use the speed control motor to drive the bakelite disc, fix some steel pieces on the disc, adjust the distance between the switch sensing surface and the action piece, about 80% of the switch action distance, rotate the disc , in turn, bringing the action piece closer to the proximity switch,
A speed measuring device is mounted on the main shaft of the disc, and the output signal of the switch is shaped and connected to the digital frequency meter. At this time, the motor is started, and the rotation speed is gradually increased. Under the condition that the product of the rotation speed and the action piece is equal to the frequency count, the frequency of the switch can be directly read by the frequency meter.
4.2.5. Repeating accuracy measurement; the action piece is fixed on the measuring tool, and the moving speed is controlled at 0.1 mm/s from the action area of ​​the switch sensing surface facing the switch from the switch operating distance of 120%. When the switch is activated, read the reading on the gauge and then back
Exit the action zone and disconnect the switch. This is repeated 10 times, and finally the difference between the maximum value and the minimum value of 10 measurements and the 10 times average value is calculated, and the difference is the repeat precision error.
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